In an electric motor car which runs on an electric power supply from a power source such as an overhead contact line, a main motor is activated as a generator and a regenerated current from the generator is returned to the overhead contact line etc. Thereby, a regenerative brake control, which has same function with a status where a car is braked, is used.
Further, in recent years, a battery may be mounted on the conventional electric motor car. In this kind of electric motor car, batteries are respectively installed in plural trailer cars constituting the electric motor car. The respective batteries mounted on the respective trailer cars in a distributed state are connected in parallel to each other through a power line, and the power line is drawn through the train. At this time, since the battery voltage is too low with respect to the driving performance of the vehicle, the battery voltage is increased to a high voltage by a step-up chopper installed inside the vehicle when the vehicle starts to run. That is, the step-up chopper applies a battery voltage increased up to a rated voltage necessary for an inverter that generates power for driving the motor. Such a technology of driving the electric motor car through the power line and the step-up chopper has been proposed. The above mentioned technology is disclosed in Japanese Patent Application Laid-Open No. 2001-352607, and contents of which are hereby incorporated by reference. Further, when the regenerated current is generated from the main motor, drive control of decreasing the main circuit voltage and returning the regenerated current to the battery are performed.